Fuel tank depressurization before refueling a plug-in hybrid vehicle

ABSTRACT

A method for operating a vehicle system is provided. The method includes monitoring a change in a temperature of the fuel vapor canister coupled to a fuel tank via a canister temperature sensor and adjusting operation of a fuel tank isolation valve based on the change in temperature of the fuel vapor canister.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 13/906,187, entitled “FUEL TANK DEPRESSURIZATIONBEFORE REFUELING A PLUG-IN HYBRID VEHICLE,” filed May 30, 2013, theentire contents of which are hereby incorporated by reference for allpurposes.

FIELD

The field of the present disclosure relates to motor vehicle fuelsystems.

BACKGROUND/SUMMARY

It may be desirable to vent fuel tanks to reduce pressure therein toreduce the likelihood of overpressure conditions in the fuel tank.Venting the fuel tank may include flowing air/vapors to a fuel vaporcanister and/or venting fuel vapors via a fuel cap. In the case of plugin hybrid vehicles, the internal combustion engine may not operate for aprolonged period of time. In such systems, the fuel tank are sealed andcan reach high pressures, necessitating additional venting operation andfurther exacerbating the aforementioned problem of fuel tankover-pressurization. Fuel tank sensors may be used as an indicator forventing operation. Venting operation may rely upon pressure sensorspositioned in the fuel tank. The pressure sensors in the vehicle's fueltank can fail, leading to problems such as fuel tank over-pressurizationand subsequent fuel tank degradation and in some case failure.

The inventors herein have recognized an issue with the above type ofsystems and developed a method for operating a vehicle system. Themethod includes monitoring a change in a temperature of the fuel vaporcanister coupled to a fuel tank via a canister temperature sensor andadjusting operation of a fuel tank isolation valve based on the changein temperature of the fuel vapor canister. It will be appreciated thatthe change in temperature of the fuel vapor canister can be correlatedto a fuel tank pressure. This correlation can be useful when a fuel tankpressure sensor is degraded. Therefore, the aforementioned method may beimplemented subsequent to fuel tank pressure sensor degradation, in oneexample. Consequently, venting operation, implemented via opening andclosing of the fuel tank isolation valve, can rely upon multiple sensors(i.e., a fuel tank pressure sensor as well as a fuel vapor canistertemperature sensor), increasing the reliability of and improving ventingoperation in the vehicle system. In another example, the monitoredchange in temperature of the fuel vapor canister can be used todetermine fuel tank pressure sensor functionality. In this way, thetemperature sensor can also be used to improve fuel tank pressure sensordiagnostics.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an example vehicle propulsion system.

FIG. 2 shows an example vehicle system with a fuel system.

FIG. 3 shows an example method for unlocking a fuel cap in accordancewith the disclosure.

FIG. 4 illustrates an example method for unlocking a fuel cap inaccordance with the disclosure.

FIG. 5 shows an example method for operating a vehicle system.

FIG. 6 shows another example method for operating a vehicle system.

FIG. 7 shows another example method for operating a vehicle system.

FIG. 8 shows a graph depicting the correlation between a fuel vaporcanister temperature, a fuel tank pressure, and a duty cycle of the fueltank isolation valve.

DETAILED DESCRIPTION

The following description relates to systems and methods for operating avehicle system based on a change in temperature of a fuel vaporcanister. The vehicle includes an engine system with a fuel system, asshown in FIG. 2, where the fuel system includes a fuel tank and a fuelcap with a locking mechanism configured to prevent the fuel cap frombeing opened. The fuel tank may be depressurized in order prevent fueldischarging from a fuel filler pipe during refueling. As such, the fuelcap may remain locked until the fuel tank is sufficiently depressurized.As described below with reference to FIGS. 3 and 4, following arefueling request the fuel tank may be vented to a fuel vapor canisterand the temperature in the fuel vapor canister may be monitored toassist in determining when the fuel tank is sufficiently depressurizedso that refueling may be performed. For example, a predeterminedtemperature change in the fuel vapor canister may be used to detect whenthe fuel tank has depressurized. In some examples, such detection mayoccur in the absence of a fuel tank pressure sensor, or when a fuel tankpressure sensor has degraded. In another aspect of the solution, thedetection may also occur alternatively, or in addition to the featuresnoted above, in response to both a pressure sensor and detection of apredetermined temperature change in the canister. Further in someexamples, the pressure in the fuel tank may be inferred from thetemperature of the fuel vapor canister and a fuel tank isolation valvemay be adjusted based on the fuel tank pressure inference. In this way,the fuel tank pressure can be inferred to improve fuel tank isolationvalve operation in the case of fuel tank pressure sensor degradation orfailure.

Turning now to the figures, FIG. 1 illustrates an example vehiclepropulsion system 100. Vehicle propulsion system 100 includes a fuelburning engine 110 and a motor 120. As a non-limiting example, engine110 comprises an internal combustion engine and motor 120 comprises anelectric motor. Motor 120 may be configured to utilize or consume adifferent energy source than engine 110. For example, engine 110 mayconsume a liquid fuel (e.g., gasoline) to produce an engine output whilemotor 120 may consume electrical energy to produce a motor output. Assuch, a vehicle with propulsion system 100 may be referred to as ahybrid electric vehicle (HEV).

Vehicle propulsion system 100 may utilize a variety of differentoperational modes depending on operating conditions encountered by thevehicle propulsion system. Some of these modes may enable engine 110 tobe maintained in an off state (i.e. set to a deactivated state) wherecombustion of fuel at the engine is discontinued. For example, underselect operating conditions, motor 120 may propel the vehicle via drivewheel 130 as indicated by arrow 122 while engine 110 is deactivated.

During other operating conditions, engine 110 may be set to adeactivated state (as described above) while motor 120 may be operatedto charge energy storage device 150. For example, motor 120 may receivewheel torque from drive wheel 130 as indicated by arrow 122 where themotor may convert the kinetic energy of the vehicle to electrical energyfor storage at energy storage device 150 as indicated by arrow 124. Thisoperation may be referred to as regenerative braking of the vehicle.Thus, motor 120 can provide a generator function in some embodiments.However, in other embodiments, generator 160 may instead receive wheeltorque from drive wheel 130, where the generator may convert the kineticenergy of the vehicle to electrical energy for storage at energy storagedevice 150 as indicated by arrow 162.

During still other operating conditions, engine 110 may be operated bycombusting fuel received from fuel system 140 as indicated by arrow 142.For example, engine 110 may be operated to propel the vehicle via drivewheel 130 as indicated by arrow 112 while motor 120 is deactivated.During other operating conditions, both engine 110 and motor 120 mayeach be operated to propel the vehicle via drive wheel 130 as indicatedby arrows 112 and 122, respectively. A configuration where both theengine and the motor may selectively propel the vehicle may be referredto as a parallel type vehicle propulsion system. Note that in someembodiments, motor 120 may propel the vehicle via a first set of drivewheels and engine 110 may propel the vehicle via a second set of drivewheels.

In other embodiments, vehicle propulsion system 100 may be configured asa series type vehicle propulsion system, whereby the engine does notdirectly propel the drive wheels. Rather, engine 110 may be operated topower motor 120, which may in turn propel the vehicle via drive wheel130 as indicated by arrow 122. For example, during select operatingconditions, engine 110 may drive generator 160, which may in turn supplyelectrical energy to one or more of motor 120 as indicated by arrow 114or energy storage device 150 as indicated by arrow 162. As anotherexample, engine 110 may be operated to drive motor 120 which may in turnprovide a generator function to convert the engine output to electricalenergy, where the electrical energy may be stored at energy storagedevice 150 for later use by the motor.

Fuel system 140 may include one or more fuel storage tanks 144 forstoring fuel on-board the vehicle. For example, fuel tank 144 may storeone or more liquid fuels, including but not limited to: gasoline,diesel, and alcohol fuels. In some examples, the fuel may be storedon-board the vehicle as a blend of two or more different fuels. Forexample, fuel tank 144 may be configured to store a blend of gasolineand ethanol (e.g., E10, E85, etc.) or a blend of gasoline and methanol(e.g., M10, M85, etc.), whereby these fuels or fuel blends may bedelivered to engine 110 as indicated by arrow 142. Still other suitablefuels or fuel blends may be supplied to engine 110, where they may becombusted at the engine to produce an engine output. The engine outputmay be utilized to propel the vehicle as indicated by arrow 112 or torecharge energy storage device 150 via motor 120 or generator 160.

In some embodiments, energy storage device 150 may be configured tostore electrical energy that may be supplied to other electrical loadsresiding on-board the vehicle (other than the motor), including cabinheating and air conditioning, engine starting, headlights, cabin audioand video systems, etc. As a non-limiting example, energy storage device150 may include one or more batteries and/or capacitors.

Control system 190 may communicate with one or more of engine 110, motor120, fuel system 140, energy storage device 150, and generator 160. Aswill be described by the process flow of FIG. 3, control system 190 mayreceive sensory feedback information from one or more of engine 110,motor 120, fuel system 140, energy storage device 150, and generator160. Further, control system 190 may send control signals to one or moreof engine 110, motor 120, fuel system 140, energy storage device 150,and generator 160 responsive to this sensory feedback. Control system190 may receive an indication of an operator requested output of thevehicle propulsion system from a vehicle operator 102. For example,control system 190 may receive sensory feedback from pedal positionsensor 194 which communicates with pedal 192. Pedal 192 may referschematically to a brake pedal and/or an accelerator pedal. In oneexample, the control system 190 may be referred to as a controlsub-system when it is incorporated into another vehicle system, such asthe vehicle system 206, shown in FIG. 2 and discussed in greater detailherein.

Energy storage device 150 may periodically receive electrical energyfrom a power source 180 residing external to the vehicle (e.g., not partof the vehicle) as indicated by arrow 184. As a non-limiting example,vehicle propulsion system 100 may be configured as a plug-in hybridelectric vehicle (HEV), whereby electrical energy may be supplied toenergy storage device 150 from power source 180 via an electrical energytransmission cable 182. During a recharging operation of energy storagedevice 150 from power source 180, electrical transmission cable 182 mayelectrically couple energy storage device 150 and power source 180.While the vehicle propulsion system is operated to propel the vehicle,electrical transmission cable 182 may disconnected between power source180 and energy storage device 150. Control system 190 may identifyand/or control the amount of electrical energy stored at the energystorage device, which may be referred to as the state of charge (SOC).

In other embodiments, electrical transmission cable 182 may be omitted,where electrical energy may be received wirelessly at energy storagedevice 150 from power source 180. For example, energy storage device 150may receive electrical energy from power source 180 via one or more ofelectromagnetic induction, radio waves, and electromagnetic resonance.As such, it should be appreciated that any suitable approach may be usedfor recharging energy storage device 150 from a power source that doesnot comprise part of the vehicle. In this way, motor 120 may propel thevehicle by utilizing an energy source other than the fuel utilized byengine 110.

Fuel system 140 may periodically receive fuel from a fuel sourceresiding external to the vehicle. As a non-limiting example, vehiclepropulsion system 100 may be refueled by receiving fuel via a fueldispensing device 170 as indicated by arrow 172. In some embodiments,fuel tank 144 may be configured to store the fuel received from fueldispensing device 170 until it is supplied to engine 110 for combustion.In some embodiments, control system 190 may receive an indication of thelevel of fuel stored at fuel tank 144 via a fuel level sensor. The levelof fuel stored at fuel tank 144 (e.g., as identified by the fuel levelsensor) may be communicated to the vehicle operator, for example, via afuel gauge or indication in a vehicle instrument panel 196.

The vehicle propulsion system 100 may also include an ambienttemperature/humidity sensor 198, and a roll stability control sensor,such as a lateral and/or longitudinal and/or yaw rate sensor(s) 199. Thevehicle instrument panel 196 may include indicator light(s) and/or atext-based display in which messages are displayed to an operator. Thevehicle instrument panel 196 may also include various input portions forreceiving an operator input, such as buttons, touch screens, voiceinput/recognition, etc. For example, the vehicle instrument panel 196may include a refueling button 197 which may be manually actuated orpressed by a vehicle operator to initiate refueling. For example, asdescribed in more detail below, in response to the vehicle operatoractuating refueling button 197, a fuel tank in the vehicle may bedepressurized so that refueling may be performed.

In an alternative embodiment, the vehicle instrument panel 196 maycommunicate audio messages to the operator without display. Further, thesensor(s) 199 may include a vertical accelerometer to indicate roadroughness. These devices may be connected to control system 190. In oneexample, the control system may adjust engine output and/or the wheelbrakes to increase vehicle stability in response to sensor(s) 199.

FIG. 2 shows a schematic depiction of a vehicle system 206. The vehiclesystem 206 includes an engine system 208 coupled to an emissions controlsystem 251 and a fuel system 218. Emission control system 251 includes afuel vapor container or canister 222 which may be used to capture andstore fuel vapors. In some examples, vehicle system 206 may be a hybridelectric vehicle system.

The engine system 208 may include an engine 210 having a plurality ofcylinders 230. The engine 210 includes an engine intake 223 and anengine exhaust 225. The engine intake 223 includes a throttle 262fluidly coupled to the engine intake manifold 244 via an intake passage242. The engine exhaust 225 includes an exhaust manifold 248 leading toan exhaust passage 235 that routes exhaust gas to the atmosphere. Theengine exhaust 225 may include one or more emission control devices 270,which may be mounted in a close-coupled position in the exhaust. One ormore emission control devices may include a three-way catalyst, lean NOxtrap, diesel particulate filter, oxidation catalyst, etc. It will beappreciated that other components may be included in the engine such asa variety of valves and sensors.

Fuel system 218 may include a fuel tank 220 coupled to a fuel pumpsystem 221. The fuel pump system 221 may include one or more pumps forpressurizing fuel delivered to the injectors of engine 210, such as theexample injector 266 shown. While only a single injector 266 is shown,additional injectors are provided for each cylinder. It will beappreciated that fuel system 218 may be a return-less fuel system, areturn fuel system, or various other types of fuel system.

Vapors generated in fuel system 218 may be routed to an evaporativeemissions control system 251 which includes a fuel vapor canister 222via vapor recovery line 231, before being purged to the engine intake223. Fuel vapor canister 222 may include a buffer or load port 241 towhich fuel vapor recovery line 231 is coupled. Further, a temperaturesensor 243 (e.g., canister temperature sensor) may be included in fuelvapor canister 222 so that temperature changes in the fuel vaporcanister may be monitored to assist in determining when the fuel tank isdepressurized prior to refueling. The temperature sensor 243 may belocated in load port 241 of fuel vapor canister 222 or in any othersuitable location in canister 222. Fuel vapors undergo an exothermicreaction when carbon in the canister adsorbs vapor from the fuel tankthus the temperature of the fuel vapor canister, e.g., as determined bytemperature sensor 243, may increase when the fuel tank is vented to thecanister. Thus, as described below, temperature changes in the canisterwhile the fuel tank is vented thereto may be used to determine an amountof pressure in the fuel tank. Further, temperature in the fuel vaporcanister may decrease when pressure in the fuel tank is belowatmospheric pressure, e.g., during vacuum conditions, since in thisexample, the vacuum in the fuel tank draws fuel vapor from the fuelvapor canister into the tank. This decrease in temperature in thecanister while the fuel tank is vented to the canister may be used todetermine when an amount of vacuum in the fuel tank falls below athreshold vacuum. In one example, the canister temperature sensor 243may include one or more thermocouples. However, other types oftemperature sensors have been contemplated.

Vapor recovery line 231 may be coupled to fuel tank 220 via one or moreconduits and may include one or more valves for isolating the fuel tankduring certain conditions. For example, vapor recovery line 231 may becoupled to fuel tank 220 via one or more or a combination of conduits271, 273, and 275. Further, in some examples, one or more fuel tankisolation valves may be included in recovery line 231 or in conduits271, 273, or 275. Among other functions, fuel tank isolation valves mayallow a fuel vapor canister of the emissions control system to bemaintained at a low pressure or vacuum without increasing the fuelevaporation rate from the tank (which would otherwise occur if the fueltank pressure were lowered). For example, conduit 271 may include agrade vent valve (GVV) 287, conduit 273 may include a fill limit ventingvalve (FLVV) 285, and conduit 275 may include a grade vent valve (GVV)283, and/or conduit 231 may include an isolation valve 253. Further, insome examples, recovery line 231 may be coupled to a fuel filler system219. In some examples, fuel filler system may include a fuel cap 205 forsealing off the fuel filler system from the atmosphere. Refueling system219 is coupled to fuel tank 220 via a fuel filler pipe or neck 211.Further, a fuel cap locking mechanism 245 may be coupled to fuel cap205. The fuel cap locking mechanism may be configured to automaticallylock the fuel cap in a closed position so that the fuel cap cannot beopened. For example, as described in more detail below, the fuel cap 205may remain locked via locking mechanism 245 while pressure or vacuum inthe fuel tank is greater than a threshold. In response to a refuelrequest, e.g., a vehicle operator initiated request, the fuel tank maybe depressurized and the fuel cap unlocked after the pressure or vacuumin the fuel tank falls below a threshold.

A fuel tank pressure transducer (FTPT) 291, or fuel tank pressuresensor, may be included between the fuel tank 220 and fuel vaporcanister 222, to provide an estimate of a fuel tank pressure. Asdescribed below, in some examples, during engine off conditions sensor291 may be used to monitor changes in pressure and/or vacuum in the fuelsystem to determine if a leak is present. The fuel tank pressuretransducer may alternately be located in vapor recovery line 231, purgeline 228, vent line 227, or other location within emission controlsystem 251 without affecting its engine-off leak detection ability. Asanother example, one or more fuel tank pressure sensors may be locatedwithin fuel tank 220.

Emissions control system 251 may include one or more emissions controldevices, such as one or more fuel vapor canisters 222 filled with anappropriate adsorbent, the canisters are configured to temporarily trapfuel vapors (including vaporized hydrocarbons) during fuel tankrefilling operations and “running loss” (that is, fuel vaporized duringvehicle operation). In one example, the adsorbent used is activatedcharcoal. Emissions control system 251 may further include a canisterventilation path or vent line 227 which may route gases out of thecanister 222 to the atmosphere when storing, or trapping, fuel vaporsfrom fuel system 218.

Vent line 227 may also allow fresh air to be drawn into canister 222when purging stored fuel vapors from fuel system 218 to engine intake223 via purge line 228 and purge valve 261. For example, purge valve 261may be normally closed but may be opened during certain conditions sothat vacuum from engine intake 244 is provided to the fuel vaporcanister for purging. In some examples, vent line 227 may include an airfilter 259 disposed therein upstream of a canister 222.

Flow of air and vapors between canister 222 and the atmosphere may beregulated by a canister vent valve 229. Canister vent valve may be anormally open valve so that fuel tank isolation valve 253 may be used tocontrol venting of fuel tank 220 with the atmosphere. For example, inhybrid vehicle applications, isolation valve 253 may be a normallyclosed valve so that by opening isolation valve 253, fuel tank 220 maybe vented to the atmosphere and by closing isolation valve 253, fueltank 220 may be sealed from the atmosphere. In some examples, isolationvalve 253 may be actuated by a solenoid so that, in response to acurrent supplied to the solenoid, the valve will open. For example, inhybrid vehicle applications, the fuel tank 220 may be sealed off fromthe atmosphere in order to contain diurnal vapors inside the tank sincethe engine run time is not guaranteed. Thus, for example, isolationvalve 253 may be a normally closed valve which is opened in response tocertain conditions. For example, isolation valve 253 may be commandedopen following a refueling request in so that the fuel tank isdepressurized prior to refueling, as described below.

The vehicle system 206 may further include a control sub-system 214.Control system 214 is shown receiving information from a plurality ofsensors 216 (various examples of which are described herein) and sendingcontrol signals to a plurality of actuators 281 (various examples ofwhich are described herein). As one example, sensors 216 may includeexhaust gas sensor 237 located upstream of the emission control device,temperature sensor 233, pressure sensor 291, and canister temperaturesensor 243. Other sensors such as pressure, temperature, air/fuel ratio,and composition sensors may be coupled to various locations in thevehicle system 206. As another example, the actuators may include fuelinjector 266, throttle 262, fuel tank isolation valve 253, pump 292,purge valve 261, canister vent valve 229, fuel pump system 226, and fuelcap locking mechanism 245. The control system 214 may include acontroller 212. The controller may receive input data from the varioussensors, process the input data, and trigger the actuators in responseto the processed input data based on instruction or code programmedtherein corresponding to one or more routines. An example controlroutine is described herein with regard to FIG. 3.

The control system 214 (e.g., control sub-system) may be configured tomonitor a change in a temperature of the fuel vapor canister via sensorscoupled to the fuel vapor canister and adjust operation of the fuel tankisolation valve based on the change in temperature of the fuel vaporcanister. Additionally in one example, the control system 214 may beconfigured to determine the functionality of a fuel tank pressure sensorbased on the monitored temperature of the fuel vapor canister. Furtherin one example, the operation of the fuel tank isolation valve may alsobe adjusted based on an exhaust gas sensor signal such as a signal fromthe exhaust gas sensor 237.

FIG. 3 shows an example method 300 for controlling a locking mechanismon a fuel cap for refueling a fuel tank in a vehicle. In particular, afuel cap may be maintained locked or in a closed position until arefueling request is generated and the fuel tank is sufficientlydepressurized before refueling. In order to determine when the fuel capmay be unlocked or opened, pressure in the fuel tank may be monitored todetermine when a pressure or vacuum in the fuel tank reaches asufficiently low level so that the fuel cap may be opened for refueling.

At 302, method 300 may include determining if the vehicle is operatingin an electric mode. For example, the vehicle may be a plug-in hybridelectric vehicle which may be operated in an electric mode with theengine-off. If the vehicle is not operating in electric mode at 302,method 300 proceeds to 306 described below. However, if the vehicle isoperating in electric mode at 302, method 300 proceeds to 304. At 304,method 300 includes ceasing purging of fuel vapors from the fuel tankinto an internal combustion engine when the vehicle is operating in anelectric mode. For example, a fuel vapor purge valve 261 may be closedor maintained closed so that fuel vapors from the fuel tank are notdelivered to the engine. Further, while operating in electric mode, thefuel tank may be sealed off from a fuel vapor canister and theatmosphere so that diurnal fuel vapors are contained in the fuel tank.In the case of plug in hybrid vehicles, the internal combustion enginemay not operate for a prolonged period of time. In such systems, thefuel tank may be sealed and at a relatively high pressure.

At 306, method 300 includes determining if entry conditions are met.Entry conditions may include engine off conditions when an engine of thevehicle is not in operation. For example, the vehicle may be a hybridelectric vehicle operating in an engine off mode and being powered bybatteries in the vehicle. As another example, entry conditions mayinclude a key-off event wherein the vehicle is turned off, e.g., wherethe vehicle is parked or is not in use and the engine is not running.Entry conditions may be further based on temperatures in the fuel systemor evaporative emission control system, e.g., entry conditions duringengine-off conditions may be based on a temperature in the fuel systemless than a threshold temperature or greater than a thresholdtemperature. For example, entry conditions may include determining if atemperature in the fuel system is in a predetermined range oftemperatures.

If entry conditions are met at 306, method 300 proceeds to 308. At 308,method 300 includes determining if a refuel request occurs. For example,a refuel request may comprise a vehicle operator depression of a button,e.g., refueling button 197, on a vehicle instrument panel in thevehicle, e.g., instrument panel 196. Thus, the refuel request mayinclude manually requesting opening of a fuel cap coupled to the fueltank. For example, a vehicle operator may provide input to the vehiclesystem indicating a desire to refuel the vehicle. If a refuel requestoccurs at 308, method 300 proceeds to 310.

At 310, method 300 includes venting the fuel tank. For example, the fueltank may be vented into a vapor absorbent canister, e.g., canister 222,in response to a request to refuel so that the pressure or vacuum in thefuel tank is decreased to a predetermined level in preparation forrefueling. For example, the fuel tank may be vented into the vaporabsorbent canister through an isolation valve, e.g., isolation valve 253may be opened.

At 312, method 300 may include determining if a pressure sensor isdegraded. For example, a pressure sensor in the fuel system or in thefuel tank, e.g., sensor 291, may be used to monitor pressure in the fueltank to determine when the fuel tank is sufficiently depressurized forrefueling. However, if a fault in the pressure sensor is identified,then pressure changes in the fuel tank may not be able to be determinedby the pressure sensor. Determining is the pressure sensor is degradedmay be based on a variety of sensor diagnostic routines, e.g., performedprior to the refueling request. If the pressure sensor is degraded at312, method 300 proceeds to 314.

At 314, method 300 includes determining if a predetermined temperaturechange in the fuel vapor canister occurs. The predetermined temperaturechange in the fuel vapor canister may indicate a stabilization intemperature of the vapor absorbent canister. For example, thepredetermined temperature change in the canister may comprise aninflection in temperature of the canister. For example, an inflection intemperature of the canister may be determined based on a rate of changeof temperature in the canister switching from increasing to decreasing.As another example, the predetermined temperature change may comprise atemperature increase in the canister greater than a thresholdtemperature increase when the fuel tank is pressurized, e.g., with apressure greater than atmospheric pressure. As another example, if thefuel tank is under vacuum with a pressure less than atmosphericpressure, then the predetermined temperature change may comprise atemperature decrease in the canister greater than a thresholdtemperature decrease. These temperature changes in fuel vapor canistermay be monitored via a temperature sensor in the canister, e.g.,temperature sensor 243.

If a predetermined temperature change in the fuel vapor canister doesnot occur at 314, method 300 returns to 310 to continue venting the fueltank until the fuel tank is sufficiently depressurized. However, if apredetermined temperature change in the fuel vapor canister occurs at314, method 300 proceeds to 318 to unlock or open the fuel cap. Forexample, if a fault is identified in a pressure sensor in the fuelsystem, unlocking the fuel cap may be responsive to the fault so thatunlocking occurs based only on a temperature change in the canister whenthe pressure sensor has failed. The predetermined temperature change inthe canister may indicate that pressure in the fuel tank is at a desiredlevel so that the fuel cap may be unlocked or opened so that refuelingmay be performed.

Returning to 312, if the pressure sensor is not degraded at 312, thenthe method proceeds to 316. At 316, method 300 includes determining if apredetermined temperature change in the fuel vapor canister occursand/or if a predetermined pressure reading from the pressure sensoroccurs. In some examples, determining pressure in the fuel tank may bebased on readings from a pressure sensor in the fuel system or in thefuel tank, e.g., pressure sensor 291, and readings from a temperaturesensor in the fuel vapor canister, e.g., temperature sensor 243. Forexample, sufficient depressurization of the fuel tank may be indicatedbased on both a pressure reading in the fuel system and based on apredetermined temperature change in the canister as described above.

If the conditions of step 316 are not met, then method 300 returns to310 to continue venting the fuel tank. However, if the conditions ofstep 316 are met, then method 300 proceeds to 318 to unlock or open thefuel cap. For example, unlocking the fuel cap may be performed when botha pressure sensor and a temperature change in the fuel vapor canisterindicate pressure in the fuel tank is at a desired level.

At 320, method 300 includes determining if the refueling event iscomplete. If the refueling event is not complete at 320, then method 300proceeds to 322 to maintain the fuel cap unlocked and the fuel tankvented until the refueling event is complete. Once the refueling eventis complete at 320, method 300 proceeds to 324. At 324, method 300includes locking or closing the fuel cap, and at 326, method 300includes discontinuing venting the fuel tank. For example, afterrefueling is complete the fuel cap may be closed and locked and the fueltank isolation valve 253 may be closed to seal the fuel tank from thecanister and atmosphere.

FIG. 4 illustrates an example method, e.g., method 300 described above,for unlocking a fuel cap after the fuel tank is sufficientlydepressurized. The graph 402 in FIG. 4 shows actuation of a refuelingbutton, e.g., refueling button 197, versus time. The graph at 404 showsactuation of a fuel tank isolation valve (FTIV), e.g., valve 353, versustime. The graph 404 shows actuation of a fuel cap or fuel door or fuelcap locking mechanism, e.g., locking mechanism 245, versus time. Thegraph 408 shows canister temperature, e.g., as measured by temperaturesensor 243, as a function of time. The graph 410 shows fuel tankpressure, e.g., as measured by pressure sensor 291, versus time.

At time T1 in FIG. 4 a refueling request is generated as indicated byactuation of the refueling button. In response to the refueling request,the isolation valve is actuated to an open position to vent the fueltank to the fuel vapor canister and the atmosphere so that pressure inthe fuel tank is decreased in preparation for refueling. As shown ingraph 410, after the fuel tank is vented to the canister, pressure inthe fuel tank begins to decrease as fuel vapor is vented from the fueltank into the canister. As fuel vapor from the fuel tank is adsorbed inthe canister, the temperature in the canister begins to increase, asshown in graph 410. At time T2, a predetermined temperature change 416occurs in the canister indicating that the fuel tank is sufficientlydepressurized. For example, the predetermined temperature change may bean inflection point in the temperature change of the canister or may bean amount of temperature change in the canister greater than atemperature threshold 412, e.g., a temperature increase to the threshold412. Further, as shown in graph 414, the pressure in the fuel tankdecreases to a pressure threshold 414 indicating that the fuel tank issufficiently depressurized for refueling. Thus, at time T2, the fueldoor or cap may be actuated or unlocked, as indicated in graph 406, sothat refueling may be performed.

FIG. 5 shows a method 500 for operating an engine system. The method 500may be implemented via one or more of the engine systems described abovewith regard to FIGS. 1 and 2 or may be implemented via other suitableengine systems, in other examples. Specifically in one example, thecontrol sub-systems described above with regard to FIGS. 1 and 2 may beused to implement the steps in method 500. Additionally, the method ofFIGS. 5-6 may be performed in a vehicle system in combination with themethods of FIG. 3.

At 501 the method includes routing fuel vapors from a fuel tank into afuel vapor canister. However, in other examples fuel vapors may not berouted to the fuel vapor canister. At 502 the method includesdetermining if a fuel tank pressure sensor is degraded. Determining fueltank pressure sensor degradation may include determining that a fueltank pressure sensor has been set. Additionally or alternatively, fueltank pressure sensor degradation may be determined by comparing a signalfrom the fuel tank pressure sensor to an expected profile of the fueltank pressure sensor. If it is determined that the fuel tank pressure isnot degraded (NO at 502) the method returns to 502 or alternativelyends. However, if it is determined that the fuel tank pressure sensor isdegraded (YES at 502) the method advances to 504.

Next at 504 the method includes monitoring a change in a temperature ofa fuel vapor canister coupled to a fuel tank via a canister temperaturesensor. Monitoring the change in temperature of the fuel vapor canistermay include receiving and/or processing a signal from a canistertemperature sensor. In one example, the canister temperature sensor mayinclude one or more thermocouples. However, other types of temperaturesensors have been contemplated.

At 506 the method includes determining a fuel tank pressure based on thechange in temperature of the fuel vapor canister. In one example, thefuel vapor canister temperature can be correlated to the fuel tankpressure. In such an example, this correlation may be predeterminedprior to vehicle manufacture and stored in a lookup table in memory of acontrol system. However in other examples, alternate or additionaltechniques may be used to associate the fuel vapor canister temperatureto the fuel tank pressure. For instance, the response rate of thecanister temperature sensor may be used to determine the fuel tankpressure. Still further in other embodiments, the temperature of thefuel vapor canister may be used in conjunction with other inputs such asengine speed, ambient temperature, throttle position, fuel injectionrate, etc.

Next at 508 the method includes adjusting operation of a fuel tankisolation valve based on the change in temperature of the fuel vaporcanister. Specifically, in one example, operation of the fuel tankisolation valve may be adjusted based on the fuel tank pressuredetermined at step 506. In this way, a second sensor can be used toinfer tank pressure which can be used for subsequent venting operation,thereby decreasing the likelihood of undesirable venting operation dueto sensor failure. Consequently, venting operation reliability can beimproved.

Adjusting operation of the fuel tank isolation valve may include steps510-512. At 510 the method includes activating the fuel tank isolationvalve to control tank pressure. It will be appreciated that activatingthe fuel tank isolation valve may include sending a signal to the valveand determining if the valve responds to the signal. At 512 the methodincludes closing the fuel tank isolation valve when an increase in thetemperature of the fuel vapor canister is discontinued. Thus, the fueltank isolation valve can be closed when the temperature of the canisterplateaus. In one specific example, it may be determined that thetemperature has plateaued when a rate of change in the temperature isless than a threshold value. In yet another example, operation of thefuel tank isolation valve may also be adjusted based on an exhaust gassensor signal, to further improve isolation valve operation. Adjustingoperation of the fuel tank isolation valve may also include opening thefuel tank isolation valve when the temperature of the fuel vaporcanister indicates that the fuel tank is above a threshold pressure.

At 514 the method includes purging the fuel vapor canister into anintake system while the fuel tank isolation valve is closed. In thisway, purging operation can be implemented to reduce evaporativeemissions. It should be appreciated that when the answer to 502 is no,the routine continues to monitor for pressure sensor degradation withoutperforming any of the actions of blocks 504, 506, 508, 510, 512, and/or514. For example, the fuel tank isolation valve operation is notadjusted based on the temperature change when the answer to 502 is no,but rather based on other parameters as desired or as described aboveherein.

FIG. 6 shows a method 600 for operating an engine system. The method 600may be implemented via one or more of the engine systems described abovewith regard to FIGS. 1 and 2 or may be implemented via other suitableengine systems, in other examples. Specifically in one example, thecontrol sub-systems described above with regard to FIGS. 1 and 2 may beused to implement the steps in method 600.

At 602 the method includes infer a fuel tank pressure based on one ormore of an ambient temperature, an engine temperature, a fuel tanklevel, and an air flow. It will be appreciated that the air flow may bethe flowrate of intake air through an intake system. In this way, fueltank pressure can be inferred from a variety of variables when a fueltank pressure sensor is degraded, for example. Thus in one example, step602 may be implemented subsequent to determining that a fuel tankpressure sensor is degraded. In other examples, additional oralternative variables may be used to determine fuel tank pressure.Further in one example, the method may include routing fuel vapors fromthe fuel tank to the fuel vapor canister prior to step 602.

At 604 the method includes determining if the inferred fuel tankpressure is greater than a threshold value. In one example, thethreshold value may be predetermined. If it is determined that theinferred fuel tank pressure is not greater than the threshold value (NOat 604) the method returns to 604. However, if it is determined that theinferred fuel tank pressure is greater than the threshold value (YES at604) the method advances to 606. At 606 the method includes opening afuel tank isolation valve. As previously discussed, the fuel tankisolation valve is coupled between the fuel tank and the fuel vaporcanister. Thus, the fuel tank isolation valve is configured to meter theamount of fuel vapors flowing between the fuel tank and the fuel vaporcanister. In this way, fuel vapor can be flowed to the vapor canister,to decrease pressure in the fuel tank.

Next at 608 the method includes monitoring a change in a temperature ofthe fuel vapor canister coupled to a fuel tank via a canistertemperature sensor. Monitoring the change in temperature of the fuelvapor canister may include receiving and/or processing a signal from atemperature sensor coupled to the fuel vapor canister.

At 610 the method includes determining if the fuel vapor canistertemperature has stabilized. Specifically in one example, it may bedetermined if the fuel vapor canister temperature has plateaued.Exemplary techniques for determining a temperature plateau are discussedabove with regard to method 500.

If it is determined that the fuel vapor canister temperature has notstabilized (NO at 610) the method returns to 610. However, if it isdetermined that the fuel vapor canister temperature has stabilized (YESat 610) the method advances to 612. At 612 the method includes closingthe fuel tank isolation valve. In this way, the fuel tank isolationvalve may be adjusted based on the change in temperature of the fuelvapor canister. It will be appreciated that the fuel vapor canister maybe purged while the fuel tank isolation valve is closed, in one example.

FIG. 7 shows a method 700 for operating an engine system. The method 700may be implemented via one or more of the engine systems described abovewith regard to FIGS. 1 and 2 or may be implemented via other suitableengine systems, in other examples. Specifically in one example, thecontrol sub-systems described above with regard to FIGS. 1 and 2 may beused to implement the steps in method 700.

At 702 the method includes monitoring a change in a temperature of thefuel vapor canister coupled to a fuel tank via a canister temperaturesensor. As previously discussed, monitoring a change in temperature mayinclude receiving and/or processing a temperature sensor signal.

Next at 704 the method determines if the fuel tank pressure sensor isfunctioning. It will be appreciated that the functionality of the fueltank pressure sensor may be based on the monitored change in temperatureof the fuel canister. Specifically in one example, an expected fuelvapor canister temperature profile may be compared to the monitored fuelvapor canister temperature profile to determine fuel tank pressuresensor functionality.

If it is determined that the fuel tank pressure sensor is functioning(YES at 704) the method advances to 706. At 706 the method includesadjusting operation of the fuel tank isolation valve based on the fueltank pressure sensor.

However, if it is determined that the fuel tank pressure sensor is notfunctioning (NO at 704) the method advances to 708. At 708 the methodincludes indicating fuel tank pressure sensor degradation. In oneexample, indicating fuel tank pressure sensor degradation may includesetting a flag in the control system, triggering a pressure sensordegradation indicator, etc.

Next at 710 the method includes adjusting operation of the fuel tankisolation valve based on the change in temperature of the fuel vaporcanister. In this way, fuel tank isolation valve operation can becarried out based on a 2^(nd) sensor (i.e., the fuel vapor canistertemperature sensor when the fuel tank pressure sensor is degraded,thereby increasing the reliability of isolation valve operation.

FIG. 8 shows a first graph 800 and a second graph 802 depicting thecorrelation between the fuel vapor canister temperature and the fueltank pressure. The first graph 800 shows a plot 804 of the fuel vaporcanister temperature sensor, the second graph 802 shows a plot 806 ofthe fuel tank pressure. A third graph 803 shows a plot 808 of a dutycycle of the fuel tank isolation valve. As shown, the plots 804 and 806have an inverse correlation.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

In another representation a method comprises, via an electroniccontroller in combination with an engine and fuel system, routing fuelvapors from a fuel tank into a fuel vapor canister; and when (or inresponse to) a fuel tank pressure sensor is degraded, monitoring achange in a temperature of the fuel vapor canister to determine ifpressure in the fuel tank is below a threshold. The temperature changemay be monitored via a temperature sensor coupled in the fuel vaporcanister measuring an internal temperature of the canister. The fueltank pressure sensor degradation may be determined in various ways, suchas based on whether the fuel tank pressure changes agree with fuel tanktemperature changes of a fuel tank temperature sensor. In response tothe determined fuel tank pressure being below the threshold, variousactions may be taken including setting a diagnostic code and sending avisual message to a vehicle operator.

In another representation, a method comprises routing fuel vapors from afuel tank into a fuel vapor canister; and in response to a fuel tankpressure sensor being determined as degraded via a control system incombination with the engine and fuel system, indicating that pressure inthe fuel tank is at a desired level based on a change in a temperatureof the fuel vapor canister. Again, various actions may be taken inresponse to the indication including performing a leak test, adjustingengine operation, and/or adjusting vehicle operation. In still anotherrepresentation a method comprises, in response to a refuel request,venting a fuel tank into a fuel vapor canister to depressurize the fueltank; and if a fuel tank pressure sensor is determined to be degraded,unlocking a fuel cap only after a stabilization in a temperature of thefuel vapor canister. In yet another representation, a method compriseswhen a fuel tank pressure sensor is degraded, inferring fuel tankpressure based on one or more of ambient temperature, enginetemperature, fuel level indicator, and air flow; and if inferred fueltank pressure is greater than a threshold, performing each of opening atank pressure control valve, monitoring a canister temperature; andclosing the tank pressure control valve only after the canistertemperature is stabilized, for example it has reached a level that doesnot change by more than 5% over a threshold duration, such as 1 minute.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for operating a vehicle system comprising: monitoring a change in a temperature of a fuel vapor canister coupled to a fuel tank via a canister temperature sensor; and adjusting operation of a fuel tank isolation valve based on the change in temperature of the fuel vapor canister.
 2. The method of claim 1, further comprising determining a fuel tank pressure based on the change in temperature of the fuel vapor canister.
 3. The method of claim 2, where a response rate of the canister temperature sensor is used to determine the fuel tank pressure.
 4. The method of claim 2, where monitoring the change in temperature of the fuel vapor canister and determining the fuel tank pressure are implemented subsequent and in response to determining a fuel tank pressure sensor degradation.
 5. The method of claim 2, where operation of the fuel tank isolation valve is adjusted based on the determined fuel tank pressure.
 6. The method of claim 1, where adjusting operation of the fuel tank isolation valve includes closing the fuel tank isolation valve, the method further comprising purging the fuel vapor canister into an intake system while the fuel tank isolation valve is closed.
 7. The method of claim 1, further comprising determining the functionality of a fuel tank pressure sensor based on the monitored temperature of the fuel vapor canister.
 8. The method of claim 1, where adjusting operation of the fuel tank isolation valve includes closing the fuel tank isolation valve when an increase in the temperature of the fuel vapor canister is discontinued.
 9. The method of claim 1, further comprising prior to monitoring the change in temperature of the fuel vapor canister and when a fuel tank pressure sensor is degraded, inferring a fuel tank pressure based on one or more of an ambient temperature, an engine temperature, a fuel tank level, and an air flow.
 10. The method of claim 9, further comprising if the inferred temperature is greater than a threshold value, adjusting operation of a fuel tank isolation valve includes opening the fuel tank isolation valve.
 11. A vehicle system comprising: a fuel vapor canister coupled to a fuel tank; a canister temperature sensor coupled to the fuel vapor canister; a fuel tank isolation valve coupled between the fuel vapor canister and the fuel tank; and a control sub-system programmed to: monitor a change in a temperature of the fuel vapor canister via sensors coupled to the fuel vapor canister; and adjust operation of the fuel tank isolation valve based on the change in temperature of the fuel vapor canister.
 12. The vehicle system of claim 11, where the control sub-system is further configured to determine the functionality of a fuel tank pressure sensor based on the monitored temperature of the fuel vapor canister.
 13. The vehicle system of claim 11, where the operation of the fuel tank isolation valve is also adjusted based on an exhaust gas sensor signal.
 14. The vehicle system of claim 11, where the system is included in a hybrid electric vehicle.
 15. The vehicle system of claim 11, where the canister temperature sensor includes one or more thermocouples.
 16. A method, comprising: routing fuel vapors from a fuel tank into a fuel vapor canister; when a fuel tank pressure sensor is degraded, determining a fuel tank pressure based on a monitored change in temperature of the fuel vapor canister; and adjusting a fuel tank isolation valve based on the determined fuel tank pressure.
 17. The method of claim 16, where the operation of the fuel tank isolation valve is also adjusted based on an exhaust gas sensor signal.
 18. The method of claim 16, further comprising indicating that the fuel tank pressure is above a threshold pressure when it is determined that the change in temperature is above a threshold value.
 19. The method of claim 16, where adjusting operation of the fuel tank isolation valve includes closing the fuel tank isolation valve when an increase of the temperature of the fuel vapor canister is discontinued.
 20. The method of claim 16, where a response rate of the canister temperature sensor is used to determine fuel tank pressure. 